| 摘要 |
1413367 Light barrier &c SIEMENS AG 27 June 1973 [29 June 1972] 30641/73 Heading G1A In a light barrier, employing a Piezo-ceramic fixed-frequency filter 4 in an oscillator circuit 6, 7, 8 which drives an electro-luminescent diode 12 via an amplifier 10, the transmitted light is received by a photo-diode 22 connected across a choke 24 supplying several resonant amplifier stages coupled by further ceramic fixed-frequency filters 28, 32 and the amplified output provides an indication of any changes or interruptions in the intensity of the received radiation. The amplifier stages may be connected to a rectifier 36 and unidirectional voltage amplifier 38 which operates a relay 42 connected to an alarm or, alternatively the amplifier 38 may operate an electronic counter or be connected to the input of a process computer
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